Those at the greatest mental illness risk from marijuana use are teenagers and young adults. Your chances of developing schizophrenia decline dramatically by your late 20s. In the course of discussions in email, quite a number of people have made the argument that decriminalizing marijuana would actually make marijuana less available to minors than it is now.

My first reaction when I first heard this claim made by William F. Buckley, Jr. many years ago was skepticism. Generally, making something illegal reduces consumption, not because potential consumers obey the law, but because illegality makes it harder to find the product. Run an ad or open a storefront selling an illegal product, and you will not be in business very long. The harder it is to find sellers, the less competitive prices will be. As the price of a commodity rises, it usually reduces demand for that commodity. There are other, very destructive effects from making it unlawful, but no advertising and rising prices will reduce demand.

Prohibition is actually one of the better illustrations of this. Cirrhosis of the liver is overwhelmingly caused by alcohol abuse -- by some estimates, 95% of cirrhosis of the liver deaths are alcohol-induced. In the years before national Prohibition took effect in 1920, a number of states had passed state-level bans on sale and possession of alcohol. And what happened to cirrhosis of the liver death rates as states passed those bans?

Unsurprisingly, cirrhosis of the liver death rates started to rise (slowly) as Prohibition came to an end. The graph of alcohol consumption for the post-Prohibition period matches up quite well with the cirrhosis of the liver death rates. The most obvious conclusion is that Prohibition reduced alcohol consumption -- and its repeal started it back up again. Whether you think Prohibition was “the noble experiment” or a completely stupid nanny-state idea, it does appear that it reduced alcohol consumption. What a surprise: laws do influence behavior.

A recurring claim is that marijuana is more available to teenagers than alcohol. Why? Because alcohol, while regulated, is a legal product to sell. Those in the business of selling alcohol are terribly concerned about losing their licenses to sell, fines, even jail time -- and so they have strong incentives to not sell to minors. Marijuana dealers, on the other hand, are already criminals -- what is the government going to do to them for selling to kids?

This is a very logical argument. If we were making laws for Vulcans, instead of mere Earthlings, this impeccable logic would lead to a beautiful result: decriminalizing marijuana would make it less available to teenagers. There is one little problem: an ounce of experience outweighs a pound of theory. Here’s a recent Idaho Statesman article about what happened when the Boise Police Department went out to “sting” bars, restaurants, and stores by having minors go in to buy alcohol: “Two teams of police officers and 18- and 19-year-old teens visited 36 businesses over the weekend. Boise police say employees served the teens alcohol at eight of those businesses -- five convenience stores, two restaurants, and a bar.” Even worse, four of the eight violations happened after employees had checked the buyer’s ID that clearly showed that the buyer was underage.